Optical Power Modulation Vital Sign Detection Method and Measurement Device

ABSTRACT

A vital sign measurement device includes a sensor fixation device, a sensor frame, an optical sensing system, and an output unit. The sensor fixation device is adapted to be placed against an anatomical location of a subject. The optical sensing system includes an optical waveguide, an optical source device to supply optical energy to the optical waveguide, and an optical detector to detect an amount of optical energy exiting the optical waveguide. The optical sensing system is adapted to sense an arterial pulse from the compression or flexing of at least a portion of the optical waveguide resulting in reduction of the amount of light exiting the optical waveguide. The output unit is configured to receive a signal indicative of the amount of light exiting the optical waveguide and to generate a measure of the vital sign based at least in part on the received signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims and claims priority toU.S. application Ser. No. 11/944,092, filed on Nov. 21, 2007, whichclaims priority to U.S. Provisional Patent Application Ser. No.60/898,269, filed Jan. 31, 2007, and to U.S. Provisional PatentApplication Ser. No. 60/998,745, filed Oct. 15, 2007, which are hereinincorporated by reference in their entirety.

TECHNICAL FIELD

This invention relates to detecting vital signs, and more particularlyto a vital sign measurement device.

BACKGROUND

Blood pressure refers to the force exerted by circulating blood on thewalls of blood vessels and constitutes one of the principal vital signs.The systolic pressure is the peak pressure in the arteries, which occursnear the beginning of the cardiac cycle. The diastolic pressure is thelowest pressure, which is at the resting phase of the cardiac cycle. Theaverage pressure throughout the cardiac cycle is reported as the meanarterial pressure. The pulse pressure reflects the difference betweenthe maximum and minimum pressures measured.

Blood pressures can be measured invasively (by penetrating the skin andmeasuring inside the blood vessels) or non-invasively. The former isusually restricted to a hospital setting. The non-invasive auscultatoryand oscillometric methods are simpler and quicker than invasive methods,have less complications, and are less unpleasant and less painful forthe patient. Non-invasive measurement methods are more commonly used forroutine examinations and monitoring.

The auscultatory method typically uses a stethoscope and asphygmomanometer. An inflatable cuff is placed around the upper arm atroughly the same vertical height as the heart and pneumaticallyconnected to a mercury manometer or aneroid gauge. The mercury manometermeasures the height of a column of mercury, giving an absolute cuffpressure measurement without need for calibration and consequently notsubject to the errors and drift of calibration which affect otherpressure gauges. The cuff is inflated manually by repeatedly squeezing arubber bulb until the brachial artery is completely occluded. Whilelistening with the stethoscope over the brachial artery distal to thepressurized cuff, the examiner slowly releases the pressure in the cuff.When blood just starts to flow in the artery, the turbulent flow createsa “whooshing” or pounding sound (first Korotkoff sounds). The pressureat which this sound is first heard is the systolic blood pressure. Thecuff pressure is further released until no sound can be heard (fifthKorotkoff sound), at the diastolic blood pressure.

Oscillometric methods are sometimes used for continuous monitoring andsometimes for making a single measurement. The equipment is functionallysimilar to that of the auscultatory method but does not rely on the useof a stethoscope and an examiner's ear. Instead, the detection means isa pressure sensor that is pneumatically connected to the cuff andregisters the (relatively small) oscillations in cuff pressure that aresynchronous with the arterial pressure waveform. The first oscillationin cuff pressure does not occur at the systolic pressure, but at a cuffpressure substantially above systolic pressure. The cuff is initiallyinflated to a pressure in excess of the systolic blood pressure. Thecuff pressure is then gradually reduced. The values of systolic anddiastolic pressure are calculated from the different oscillationamplitudes that occur at various cuff pressures by the use of analgorithm. Algorithms used to calculate systolic and diastolic pressureoften use experimentally obtained coefficients aimed at matching theoscillometric results to results obtained by using the auscultatorymethod as well as possible.

SUMMARY

In some aspects, a vital sign measurement device includes a sensorfixation device, a sensor frame held by the sensor fixation device, anoptical sensing system held by the sensor frame, and an output unit. Thesensor fixation device is adapted to be placed against an anatomicallocation of a subject, within which is an artery. The optical sensingsystem includes an optical waveguide, an optical source device to supplyoptical energy to the optical waveguide, and an optical detector todetect an amount of optical energy exiting the optical waveguide. Theoptical sensing system is adapted to sense an arterial pulse from thecompression or flexing of at least a portion of the optical waveguide,which results in reduction of the amount of optical energy exiting thesecond end of the optical waveguide. The output unit is configured toreceive a signal indicative of the amount of light exiting the opticalwaveguide and to generate a measure of the vital sign based at least inpart on the received signal.

The vital sign measurement device operates on the principle of opticalpower modulation, namely that an arterial pulse can cause the flexing orcompression of an optical waveguide to result in a change in an amountof optical energy transmitted to the second end of the opticalwaveguide. By monitoring the amount of light that exits the second endof the optical waveguide, data regarding the arterial pulse can beobtained and used to determine various vital signs. The optical sensingsystem can be configured to detect optical signals representative of aseries of arterial pulses and the output unit can be adapted todetermine a pulse waveform for each of the series of arterial pulsesbased on the amount of optical energy exiting the second end of theoptical waveguide. The optical sensing system can be adapted to sensethe pulsatile opening of the artery by the compression and flexing ofthe compressible optical waveguide resulting in a pulsatile decrease inan amount of detected light. The optical detector can be opticallycoupled to the optical waveguide such that the optical detector receivessubstantially all of the optical energy from the optical source thatdoes not escape from the sides of the optical waveguide. The opticalsource can include a coherent light source.

In some implementations, the sensor fixation device can be a cuffincluding an inflatable bladder within the cuff. The inflatable bladdermay partially encircles the limb. The cuff can be made of a fabricmaterial. The cuff can be adapted to apply pressure to the anatomicallocation and thereby compress an artery within the anatomical location.For example, the cuff can apply pressure when the inflatable bladder isinflated. The sensor frame can be attached to the cuff at a locationthat is not coincident with any part of the bladder. The sensor framecan be held in opposition to the limb by its attachment to the cuff suchthat the pressure applied to the limb by the sensor frame issubstantially equal to the pressure applied to the limb by thesurrounding cuff when the inflatable bladder is inflated.

In some implementations, the device can include a sensor pad within thesensor frame, which can be positioned adjacent to the anatomicallocation. The sensor pad can be configured such that it moves as aresult of increased contact pressure caused by the inflation of thebladder. The movement of the sensor pad can result in the compression orflexing of the optical waveguide. In some implementations, the sensorpad can be positioned at a midpoint of the sensor fixation device. Inother implementations, the sensor pad can be positioned at a distallocation of the sensor fixation device. In some implementations, thesensor pad can be configured such that pulsatile tensioning of thesensor fixation device does not produce pulsatile movement of the sensorpad, whereas pulsatile opening of the artery within the anatomicallocation produces a pulsatile movement of the sensor pad. In someimplementations, a maximum contact pressure applied to the sensor padcan cause a reduction of 20-80% (e.g., a 50-70% reduction) in the totalamount of light exiting the optical waveguide.

In some implementations, the device can include a load spring attachedto at least a portion of the sensor frame and also supporting the sensorpad. The load spring can be configured to counter at least some of thepressure exerted against the sensor pad at the anatomical location of asubject. The load spring can be adapted to allow a desirabledisplacement of the sensor pad at a maximum pressure. In someimplementations, the load spring can be adapted to provide a maximumdisplacement of the sensor pad between 0.5 and 3 millimeters at amaximum pressure.

In some implementations, the device can include a pressure sensor todetect a pressure applied to the anatomical location. The output unitcan receive a pressure input indicative of the pressure applied to theanatomical location from the pressure sensor. In some implementations,the output unit can generate the vital sign using the signal indicativeof the optical signal received and the pressure input.

In some implementations, the anatomical location of the subject is anupper arm. The sensor frame can be configured on the sensor fixationdevice so that the optical sensing system is positioned to sensemovement due to a pulse of a brachial artery resulting in thecompression or flexing of at least a portion of the compressible opticalwaveguide. In some implementations, the vital sign can be at least oneof a heart rate, an arterial pulse waveform, a systolic blood pressure,a diastolic blood pressure, a mean arterial blood pressure, a pulsepressure, and an arterial compliance.

In some implementations, the device can include a waveguide supportstructure having a non-compliant surface to support at least a portionof the optical waveguide. The optical sensing system can be adapted tocause a flexural deformation in an unsupported portion of the opticalwaveguide in response to an arterial pulse.

In some implementations, the device can include a flexible andincompressible support surface that supports the optical waveguide oversubstantially all of its length. For example, the waveguide supportsurface can be a flexible electronic circuit board.

The waveguide can be bonded to the support surface with a flexibleelastomer adhesive. In some implementations, the optical source device,the optical detector, and/or associated electronic components can bemounted on the surface of the waveguide support surface. In someimplementations, the waveguide support surface can include a supportreturn element which is configured within the support surface andadapted to oppose the flexing of the support surface. In someimplementations including a sensor pad, the support return element canbe adapted to provide an increasing contact pressure between the sensorpad and the optical waveguide as the sensor pad moves from a restposition to a position of maximum displacement. The optical waveguidecan be adapted such that said increasing contact pressure causes adecreasing amount of light exiting the second end of the opticalwaveguide.

In some implementations, the optical waveguide can be a compliantwaveguide including a cladding devining a lumen and a core disposedwithin the lumen. The core having a refractive index greater than therefractive index of the cladding. The cladding can have a flat surface.In some implementations, the cladding and/or the core can include anelastomer having a Shore A hardness of between 25 and 75. In someimplementations, the cladding can have a Shore A durometer of between 45and 55 and the core can have a Shore A hardness between 30 and 45. Insome implementations, the waveguide can be capable of guiding at least10,000 modes (e.g., at least 50,000 modes). In some implementations, thecore can have a refractive index between 1.43 and 1.50 (e.g., between1.45 and 1.47) and the cladding can have a refractive index between 1.39and 1.48 (e.g., between 1.39 and 1.41). In some implementations, thecore can have a radius of at least 45 micrometers (e.g., between 150 and200 micrometers).

In some implementations, the optical waveguide can include an elastomer(e.g., a siloxane elastomer). The elastomer can be selected from thegroup consisting of polysiloxane, polyurethane, polybutadine rubber, andcombinations thereof.

In some aspects, a method of measuring a vital sign in a subject caninclude transmitting optical energy into a first end of the opticalwaveguide, detecting an amount of optical energy ensiting a second endof the optical waveguide, and generating a measure of the vital signbased on the detected amount of optical energy exiting the second end toof the optical waveguide. The optical waveguide is positioned with asensor frame and the sensor frame is positioned against an anatomicallocation of a subject, within which is an artery. The optical waveguideis positioned to compress or flex in response to an arterial pulse. Theamount of optical energy exiting the second end of the optical waveguideis detected using an optical detector held by the sensor frame. Theoptical detector generates a signal indicative of an amount of opticalenergy received. The amount of optical energy exiting the second end ofthe optical waveguide changes in response to arterial pulses.

In some implementations, the sensor frame can be held by a sensorfixation device and the method can further include applying a pressureto the anatomical location of the subject with the sensor fixationdevice. In some implementations, method can further include varying thepressure applied to the anatomical location with the sensor fixationdevice over a period of time and determining a series of pulsecharacteristics for arterial pulses during the period of time fromchanges in the amount of optical energy exiting the second end of theoptical waveguide over the period of time. The generated measure of thevital sign can be based on the series of pulse characteristics duringthe period of time.

In some implementations, the method can include obtaining a measuredblood pressure measurement and then estimating a second blood pressuremeasurement. Estimating the second blood pressure measurement can bebased on an initial pulse characteristic, obtained at an initial time,and a subsequent pulse characteristic obtained as a subsequent time,used to estimate the second blood pressure measurement. The initial timeis closer to the time of the measured blood pressure estimate than thesubsequent time. The generated measurement of the vital sign is based onthe measured blood pressure measurement, the initial pulsecharacteristic, and the subsequent pulse characteristic. In someimplementations, the initial pulse characteristic and the subsequentpulse characteristics can be pulse amplitudes.

In some aspects, a method of measuring a subject's blood pressure caninclude applying a varying pressure to an anatomical location of asubject, within which is an artery, detecting an arterial pulse waveformwith an optical power modulation sensor, and determining a systolicblood pressure and a diastolic blood pressure based on the detectarterial pulse waveform as a function of the applied and variedpressure. The optical power modulation sensor includes an opticalwaveguide adapted to be compressed or flexed in response to an arterialpulse. The compression or flexing of the optical waveguide results in areduction in the amount of light transmitted to an end of the opticalwaveguide. The arterial pulse waveform being detected from the amount oflight exiting the end of the optical waveguide.

The details of one or more implementations of the invention are setforth in the accompanying drawings and the description below. Otherfeatures, objects, and advantages of the invention will be apparent fromthe description, drawings, and claims.

DESCRIPTION OF DRAWINGS

FIG. 1 depicts one implementation of the vital sign measurement device.

FIGS. 2A, 2B, and 2C depict various implementations of the vital signmeasurement device positioned on an upper arm, and showing threedifferent levels of cuff pressure relative to arterial systolicpressure.

FIG. 3 depicts a series of pulses during deflation of a cuff detected bya pressure sensor pneumatically coupled to the cuff compared tosimultaneously obtained pulses detected by an optical sensing systemheld by a sensor fixation device.

FIG. 4 depicts an implementation of a vital sign measurement devicehaving a sensor fixation device with an inflatable bladder.

FIGS. 5A, 5B, and 5C depict an implementation of an sensor framecontaining the components of an optical sensing system.

FIG. 6 depicts an implementation of the optical sensing system on aflexible an incompressible waveguide support surface.

FIGS. 7A-7C depict implementations of optical sensing systems.

FIGS. 8A and 8B depict how a compressed waveguide results in a reductionin the amount of transmitted light.

FIGS. 9A and 9B depict how a flexed waveguide results in a reduction inthe amount of transmitted light.

FIGS. 10A-10D are cross-sectional views of different implementations ofthe waveguide.

FIG. 11 depicts the pulsatile light transmission in a waveguidesubjected to an oscillating deformation due to an arterial pulse.

FIG. 12 depicts an implementation of an analytical method used todetermine one or more vital signs by the output unit.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

As shown in FIG. 1, a vital sign measurement device can include a sensorfixation device 102, a sensor frame 200 holding an optical sensingsystem, and an output unit 106. An output from the optical sensingsystem in the sensor frame 200 can be used to determine the measurementof a vital sign, for example, blood pressure of a patient, andspecifically systolic and diastolic measures for the blood pressure ofthe patient.

The sensor fixation device 102 holds the sensor frame 200 and applies itagainst an anatomical location of a subject 112, within which is anartery 118. In the FIG. 1, for example, the anatomical location 112 isan upper arm of a human patient. The sensor frame 200 can be positionedso that the optical sensing system 104 senses movement corresponding toan arterial pulse when the sensor frame 200 is placed against theanatomical location 112 of the subject. In this manner it is possible todetect arterial pulses with the optical sensing system when the sensorfixation device 102 is exerting a pressure on the subject's arm 112 thatis at or below systolic pressure, but not detect arterial pulses whenthe sensor fixation device 102 is above systolic pressure. Accordingly,systolic pressure can be determined as the pressure applied to theanatomical location 112 when the first arterial pulse is detected by theoptical sensing system, as a pressure is reduced from a pressureexceeding systolic pressure. Alternatively, systolic pressure can bedetermined to be the last pressure at which an arterial pulse isobserved by the optical sensing system, as the pressure is as thepressure is increased to a pressure exceeding systolic pressure.Furthermore, the vital sign measurement device can measure the relativestrength of one or more arterial pulses, and/or detect a pulse waveform,when the sensor fixation device is exerting a pressure of less thansystolic pressure on the patient's arm, and from those measurements,determine a number of different vital sign measurements includingsystolic and diastolic pressure measurements for the subject. Forexample, diastolic pressure can be determined based on predeterminedpulse waveform characteristis, such as a ratio of pulse amplitudesand/or the shape of the pulse waveform between arterial pulses.

The optical sensing system 104 employs what may be referred to as anoptical power modulation method to detect and measure arterial pulses.An example optical sensing system that implements such an optical powermodulation method, referring in particular to FIG. 5C, includes anoptical waveguide 212 held by the sensor frame 200, an optical source202 positioned to supply optical energy to a first end of the opticalwaveguide 212, and an optical detector 240 positioned to detect anamount of optical energy exiting a second, opposite end of the opticalwaveguide 212. An output unit 106, for example as shown in FIG. 1, isconnected so as to receive a signal, for example an electrical signal,from the optical sensing system, and in particular from the opticaldetector 240, wherein the signal is indicative of an amount of light ata given point in time exiting the second, opposite end of the opticalwaveguide that is detected by the optical detector 240. From thatreceived signal, the output unit 106 generates a measure of the vitalsign. The optical sensing system 104 is acted upon, or responds to, anarterial pulse by virtue of the compression or flexing of at least oneportion of the optical waveguide 212 of the sensing system, whichresults in a reduction to the amount of optical energy exiting theoptical waveguide and accordingly a reduction in the amount of opticalenergy received by the optical detector.

By way of example, a vital sign can include a heart rate, an arterialpulse waveform, a systolic blood pressure measure, a diastolic bloodpressure measure, a mean arterial blood pressure measure, a pulsepressure measure, and/or a measurement of arterial compliance. In someimplementations, the vital signs can be determined from the timing ofarterial pulses, the amplitude and/or magnitude of arterial pulses,and/or from arterial pulse waveforms. In some implementations, the vitalsigns can be determined from output received from the optical sensingsystem 104 alone, while in other implementations the vital signs can bedetermined from that output in combination with other data (e.g., dataregarding the pressure within a pneumatic cuff). As example of theformer case, a heart rate can be determined from the output receivedfrom the optical sensing system 104 alone. The present vital signmeasurements can be taken in any limb location, including but notlimited to the upper arm, the wrist area, the legs, and the digits.

Sensor Fixation Device

The sensor fixation device can be any structure adapted to hold andposition a sensor frame 200 or a portion thereof adjacent to ananatomical location of a subject 112 such that the optical sensingsystem 104 within the sensor frame 200 can detect an arterial pulse. Thesensor fixation device can hold the sensor frame 200 adjacent to ananatomical location of a subject 112 at a predetermined sensor fixationpressure or at an adjustable sensor fixation pressure. For example, thesensor fixation device can be an adhesive bandage or a cuff (e.g., anelastic cuff or an inflatable cuff).

As shown in FIG. 4, a sensor fixation device 102 can be an inflatablecuff 120 having an inflatable bladder 122. For example, the sensorfixation device 102 can be an assembly that includes a cuff comprising afabric material that is configured to surround or encircle an anatomicallocation (e.g., a limb) of a subject. The inflatable bladder 122 can bepositioned within the cuff to partially surround or encircle a limb. Assuch, the sensor fixation device 102 is adapted to apply pressure to thelimb when inflated and thereby compress an artery within the limb.

Generally, a cuff-type sensor fixation device 102 for use in thepresently described systems and methods can be of a type that eithercompletely or partially encircles the limb, or may be of a type thatapplies pressure locally as may be advantageous in certain anatomicallocations, including the wrist over the radial artery. The bladder 122in such a device 102 can be pneumatically connected to a pump 124 via ahose 116, as is the case in FIG. 4. In some implementations such as thatshown in FIG. 4, a pneumatically inflatable cuff can be inflated (e.g.,via a pump 124) and deflated (e.g., via a valve 126) to adjust thepressure applied to a portion of a subject's body 112. In someimplementations, a system can include an inflation controller 452, suchas is included in the output unit 106 as shown in FIG. 12, to controlthe inflation and deflation of the cuff. In other implementations, aninflation controller can be included as a separate controller unit tocontrol the operation of the vital sign measurement device.

As such, various forms of a sensor fixation device can be applied tovarious different portions of a subject's body. The sensor fixationdevice can be sized and arranged for placement at an anatomical locationof a subject's body adjacent to a predetermined artery of the subject.As shown in FIGS. 1 and 2A-2C, the sensor fixation device 102 can bepositioned on an upper arm (above a subject's elbow) so that the opticalsensing system within the sensor frame 200 can sense movementcorresponding to an arterial pulse in the brachial artery 118. Thesensor fixation device can also be adapted for placement on the wrist sothat the optical sensing system in the sensor frame can sense movementcorresponding to an arterial pulse in the radial artery. The sensorfixation device can also be positioned on a leg (e.g., at the ankle todetect pulses in an artery), the neck, or any other part of the bodywhere an arterial pulse can be detected.

As shown in FIGS. 2A-2C, the sensor frame 200 can be positioned proximalto the midpoint of the sensor fixation device 102 (as shown in FIG. 2A),at the mid point of the sensor fixation device 102 (as shown in FIGS. 2Band 2C), or distal to the mid point of the sensor fixation device 102(not shown). The placement of the sensor frame 200, and morespecifically the sensing portion (e.g., a sensor pad) of the sensorframe 200, with respect to a pressure imparting device can impact thedata obtained. In implementations where the sensor fixation device 102applies pressure to the anatomical location, such as shown in FIGS.2A-2C, the position of the sensing portion of the sensing frame 200within the sensor fixation device 102 can impact the data obtained. Insome implementations, a pressure applied to an artery lying below thesurface of an anatomical location can be non-uniform. For example,although a pressure imparting body placement device 102 can apply auniform pressure, the pressure transmitted through the layers of tissuecan result in a non-uniform pressure against an artery lying somedistance below the surface. In some implementations, the pressureapplied to an artery lying some distance below the skin by an inflatablecuff can be greatest at the cuff midline and less at the cuff margins.The location of the sensor frame 200 relative to the sensor fixationdevice 102 can be fixed to optimize the sensitivity to selected featuresof the arterial pulse. In some implementations, the sensor frame 200 andthe sensing portion (e.g., the sensor pad) of the sensor frame 200 canbe located at the midline 134 of the cuff such that it is not responsiveto pulsatile enlargement of the arterial segment under the proximal partof the cuff when the cuff pressure exceeds systolic pressure, therebyallowing a precise determination of the systolic pressure when themidsection of the arterial segment opens.

In other implementations, not shown, the sensor frame 200 and thesensing portion (e.g., a sensor pad) of the sensor frame 200 can belocated near the distal margin of the cuff such that it is responsivespecifically to the pulsatile arterial dimension changes at thatlocation. Accordingly, the unique features of the arterial pulsewaveform at diastolic pressure at a distal position can be identified,and effects of arterial compliance in more distal arteries can bedetected. Outward flexing of the skin at the midline 134 of the cuff,and also distal to the midline 134, occurs during systole when the cuffpressure is below systolic pressure. At cuff pressures exceedingsystolic blood pressure, the arterial oscillations are limited to theproximal area of the cuff, as discussed above.

In some implementations, not shown, the device can include a secondpressure imparting device separate from the sensor fixation deviceholding the sensor frame having the optical sensing system. The secondpressure imparting device can be adapted to be placed against a secondanatomical location of a subject proximal to the anatomical location ofthe sensor fixation device to allow for arterial pulse detection by theoptical sensing system at a position distal to and separated from thepressure imparting device. Accordingly, the optical sensing system candetect an arterial pulse waveform at a position spaced away and distalto the point of arterial occlusion, and thus allow for the detection ofunique features of an arterial waveform. The second pressure impartingdevice can be an inflatable cuff. In some implementations, both thepressure imparting device and the sensor fixation device can beinflatable cuffs.

FIG. 2A depicts a sensor fixation device 102 imparting a pressure on thearm exceeding arterial systolic pressure of the brachial arterysufficient to result in a minimal arterial opening under the leadingedge of the sensor fixation device 102 at systole. The amount ofpressure imparted against the sensor fixation device 102 will pulsateslightly due to the arterial expansion at the leading edge during anarterial pulse. No arterial opening occurs at the positioning of thesensor frame 200, and therefore the optical sensing system 104 in thesensor frame 200 does not produce a pulsatile signal. A pulsatilesignal, however, will occur at a higher pressure if the sensor frame 200is located at a position proximal to the midpoint of the sensor fixationdevice 102 than if it is located at the midpoint of the sensor fixationdevice 102.

FIG. 2B depicts a sensor fixation device 102 imparting a pressureslightly exceeding arterial systolic pressure, such that the arterialopening 118 extends nearly to the midpoint of the sensor fixation device102 at systole. The oscillation in pressure imparted against the sensorfixation device 102 during an arterial pulse pressure would be muchlarger than in the case of FIG. 2A, as the arterial expansion occursover nearly half of the segment located within the sensor fixationdevice. Nevertheless, no arterial opening occurs at the sensor fixationdevice 102 midpoint, and therefore the optical sensing system 104 in thesensor frame 200 does not produce a pulsatile signal.

FIG. 2C depicts a sensor fixation device 102 imparting a pressure belowarterial systolic pressure, such that the entire artery segment 118opens momentarily at systole. The oscillations in pressure impartedagainst the sensor fixation device 102 during an arterial pulse will beeven greater in amplitude. The arterial opening at the location underthe sensor frame 200 causes the optical sensing system 104 to register apulsatile signal.

The top portion of FIG. 3 depicts pressure pulses sensed in a sensorfixation device 102 imparted by the series of arterial pulses as theimparted pressure by the sensor fixation device 102 is decreased from apressure exceeding systolic blood pressure of a subject to a pressurebelow diastolic blood pressure of a subject. The bottom portion of FIG.3 depicts pulses determined from the optical sensing system with thesensor frame at the midpoint of a sensor fixation device 102 as thepressure imparted by the sensor fixation device is decreased from apressure exceeding systolic blood pressure of a subject to a pressurebelow diastolic blood pressure of a subject. As shown, the opticalsensing system within the sensor frame does not detect any pulses untilthe imparted pressure is at or below systolic blood pressure. This canallow for an accurate determination of systolic blood pressure and thewaveform detected by the optical sensing system can allow for thecalculation of other vital signs.

FIG. 4 depicts one implementation of a sensor fixation device 102. Thesensor fixation device can be an inflatable cuff 120 having aninflatable bladder 122. The cuff can include a fabric materialconfigured to surround a limb of a subject. The inflatable bladder 122can partially, but not completely, encircle the limb, and can be adaptedto apply pressure to the limb when inflated and thereby compress anartery within the limb. The inflatable cuff 120 can be adapted to bewrapped around the upper arm of a subject and to hold a sensor frame 200in a position to apply equal pressure to the limb. An optical sensingsystem can be located within the sensor frame 200 to detect arterialpulses from the brachial artery. The cuff 120 can include hook and loopfasteners 132 (e.g., Velcro®) or other fastening devices, which can beused to secure the cuff 120 around a limb of a subject. The cuff 120 canbe wrapped around a subject's limb and the bladder 122 can be inflatedto impart a pressure on the limb. The bladder 122 can be connected to apump 124 by a hose 116. The bladder 122 can also be attached to a valve126 which can control the deflation of the bladder 122. The pressure inthe bladder 122 can be measured with a pressure transducer 128. Thepressure transducer 128 can be located in the bladder, as shown, or canbe pneumatically connected to the bladder 122 (e.g., via the hose 116).

The components of the optical sensing system can be packaged within thesensor frame 200 (e.g, a housing) located at the midpoint 134 of thecuff 120. The sensor frame 200 can be attached to the cuff at a locationthat is not coincident with part of the bladder. The sensor frame 200can be in opposition on the cuff such that the pressure applied to thelimb by the sensor frame is substantially equal to the pressure appliedto the limb by the surrounding cuff fabric when the inflatable bladder122 is inflated. For example, the upper surface of the sensor frame 200can be approximately flush with an inside surface of the cuff. Thesensor frame 200 can be positioned on the cuff 120 so that the opticalsensing system 104 can sense a pulse of an artery when the cuff 120 iswrapped around an anatomical location of a patient.

Output Unit

As shown in FIGS. 4 and 12, the output unit receives signals (e.g.,electrical signals) representative of an amount of optical energy (e.g.,light) exiting the second end of the optical waveguide and thus detectedby the optical detector 240. These signals can be transmitted viaelectrical wires 108. In some implementations, the output unit 106 canalso receive other data. For example, as shown in FIG. 4, wires 108 cantransmit data in the form of signals (e.g., electrical signals) from apressure transducer in the bladder 122 of a cuff 120 to the output unit106 to allow the output unit 106 to determine an amount of pressureapplied to an anatomical location of a patient. In some implementations,the output unit 106 can receive data regarding the amount of opticalenergy received by an optical detector from the optical sensing systemvia wireless transmission.

As shown in FIGS. 1, 4, and 12, the vital sign measurement device caninclude a display unit 114 to depict one or more vital signs (e.g.,heart rate, systolic pressure, and diastolic pressure). As shown in FIG.4, the output unit 106 can be packaged with the display unit 114. Insome implementations, not shown, the output unit can be within thesensor frame, can be in another portion of the cuff assembly, or can beremotely located and in communication with the optical sensing systemvia wireless transmissions. Wires can transmit data (e.g., viaelectrical signals) from the output unit 106 to the display device 114.In other implementations, the output unit 106 can transmit vital signmeasurements via wireless transmission.

In some implementations, the output unit can include an alarm system toproduce a human detectable signal when a vital sign measurementgenerated by the output unit meets a predetermined criteria. Forexample, the output unit can be adapted to create a visual or audioalarm to alert a user that a detected vital sign is outside of apredetermined range.

The output unit 106 can perform a number of data processing steps,calculations, or estimating functions, some of which are discussedbelow. The output unit 106 can include a processor to determine thevital sign from signals from the optical sensing system with or withoutother data (e.g., data regarding a pressure applied to an anatomicallocation by an inflatable cuff as shown in FIG. 4).

Sensor Frame

As shown in FIGS. 5A, 5B, and 5C, an optical sensing system 104 can becontained within a sensing frame 200 (e.g., a housing). The function ofthe sensor frame 200 is to maintain pressure against the skin andtransmit the mechanical impulse of arterial pulses to the opticalsensing system 104 without transmitting the pneumatic cuff pressurepulse. The function of the optical sensing system 104 is to generate asignal representative of the arterial pulse.

The sensor frame 200 can be placed against an anatomical location (e.g.,against a subject's skin) to sense arterial pulses by the movement ofthe sensor pad 232, which can be positionable adjacent to the anatomicallocation. The sensor pad 232 can be configured such that it moves as aresult of increased contact pressure caused by the inflation of thebladder. The movement of the sensor pad 232 can result in thecompression or flexing of the optical waveguide 212. The sensor frame200 can also include a load spring 234 attached to the sensor pad 232 tocounter the force applied to the sensor pad 232 by the anatomicallocation of the subject. The load spring 234 can also be attached to atleast a portion of the sensor frame 200. The sensor frame 200 can alsoinclude structures to support the waveguide, such as a flexible andincompressible waveguide support surface 233, upon which the waveguiderests, and/or a non-compliant waveguide support structure 235 to supportthe optical waveguide 212 against the forces applied to the opticalwaveguide 212 by the sensor pad 232. The sensor frame 200 can alsoinclude wires 108 to transmit data from the optical detector 240 to theoutput unit 106. In some implementations, not shown, the sensor frame200 can include an output unit and can include wires that transmit datafrom the output unit to an external source (e.g., a display). In someimplementations, the sensor frame 200 can have a width of between 0.7and 1.3 inches (e.g., about 1 inch), a length of between 1.5 and 2.2inches (e.g., about 1.7 inches), and a thickness of between 0.3 and 0.9inches (e.g., about 0.6 inches).

As shown in FIGS. 5A, 5B, and 5C, a sensor pad 232 adapted for placementagainst an anatomical location of a subject can be attached to a loadspring 234. The sensor pad 232 can extend out of the sensor frame 200when in a relaxed state. For example, the sensor pad 232 can extend outof the sensor frame 200 by at least 0.1 inch (e.g., between 0.1 and 0.3inches). As shown, the sensor pad 232 extends out from the sensorhousing 200 by 0.161 inches. The sensor pad 232 can have any shape. Thesensor pad 232 can have a diameter of at least 0.3 inches, for examplebetween 0.3 and 0.8 inches (e.g., about 0.6 inches). In someimplementations, for example as shown in FIG. 5C, the sensor pad 232 canbe attached to the spring 234 by a hinge 236 that allows for the backand forth motion of the sensor pad 232. In some implementations, asshown in FIG. 5C, the sensor pad 232 can have an inclined upper surface.The sensor pad 232 can be attached to or otherwise positioned to causethe compression or flexing of the optical waveguide 212 of the opticalsensing system 104. As shown in FIG. 5C, the sensor pad 232 can includea pressing portion 238 adapted to cause the localized compression of theoptical waveguide 212. The sensor pad 232 can also be positioned withina cutout 252. The spacing between the cutout 252 and the sensor pad 232can impact the amount of movement of the sensor pad 232 allowed by thesensor housing 200 due to arterial pulses. The spacing between thecutout 252 and the sensor pad 232 can be about 0.1 inches.

Wires 108 can transmit data from the optical detector 240 to an outputunit 106, as discussed above. In some implementations, not shown, theoutput unit can be included within the sensor frame and wires cantransmit vital sign data to devices outside of the housing. In someimplementations, not shown, the optical sensing system 104 can transmitdata from the sensor frame 200 by wireless transmission.

The load spring 234 can counter a force applied to the sensor pad 232from an arterial pulse and return the sensor pad to an initial stateafter the arterial pulse. The load spring 234 can thus limit the amountof compression and flexural deformation of the waveguide due to anarterial pulse. The load spring 234 can be selected such that theoptical transmission factor is most sensitive to waveguide deformationwithin the useful range of cuff pressures. The combination of the loadspring 234 and other features of the sensor frame 200 and the opticalsensing system 104 can provide countering forces such that an appliedpressure of 150 mmHg will displace the sensor pad by at least 1 mm froma resting state. In some implementations, the sensor frame 200 andoptical sensing system 104 can be adapted such that an applied pressureof 150 mmHg will displace the sensor pad by at least 2 mm from theresting state. In some implementations, the load spring 234 can beadapted to provide a maximum displacement of the sensor pad between 0.5and 3 millimeters at a maximum pressure (e.g., between 0.8 and 1.5millimeters at a maximum pressure). In some implementations, the sensorframe 200 and optical sensing system 104 can be adapted such that anapplied pressure of between 80 and 150 mmHg (e.g., between 100 and 130mmHg) can render an upper surface of the sensor pad approximately flushwith an upper surface of the sensor frame 200. In some implementations,the sensor pad 232 can be nearly flush with the sensor frame 200 whenplaced against the anatomical location of a patient by the occludingdevice 102 with the occluding device providing a pressure to theanatomical location exceeding systolic pressure. In someimplementations, the upper surface of the sensor frame 200 can beapproximately flush with an inner surface of the sensor fixation device(e.g., the inflatable cuff).

The sensor frame 200 can also include a waveguide supporting structures,such as the flexible and incompressible waveguide support surface 233and/or a non-compliant waveguide support structure 235 to support thewaveguide 212 of the optical sensing system 104 against the forceapplied by the sensor pad 232. The waveguide support surface 233 canhave a flexible and incompressible support surface and can extend alongthe entire length of the optical waveguide 212. In some implementations,as shown in FIG. 6, the waveguide support 233 can have a support returnelement 237 configured within the support surface and adapted to opposethe flexing of the support surface. For example, the support returnelement 237 within the waveguide support 233 can be a member with a highmemory, such as a steel spring, which can return the waveguide to itsnon-deformed position following each pulsatile deformation. The supportreturn element 237 can be adapted to provide an increasing contactpressure between the sensor pad and the optical waveguide as the sensorpad moves from a rest position to a position of maximum displacement,with the optical waveguide adapted such that said increasing contactpressure causes a decreasing amount of light exiting the opticalwaveguide. In some implementations, the support return element 237 canwork with the load spring 234 to accomplish the increasing contactpressure. In some implementations, the waveguide support surface 233 canbe a flexible electronic circuit board, to which the waveguide is bondedwith a flexible elastomer adhesive. As shown in FIG. 6, the waveguidesupport surface 233 can also support and carry the optical source 202and/or the optical detector 240. In some implementations, otherassociated electronic components can be mounted on the waveguide supportsurface 233.

The waveguide support structure 235 is non-compliant. In someimplementations, as shown in FIG. 7A the waveguide support structure 235can support the portion of the waveguide 212 being acted upon by thesensor pad 232 (e.g., over substantially all of its length).Accordingly, the waveguide 212 can be compressed between the waveguidesupport 235 and pressing portion 238. FIGS. 8A and 8B, discussed below,depict how the compression of the waveguide 212 can result in areduction in the amount of light transmitted to the optical detector240. In other implementations, as shown in FIGS. 7B and 7C, thewaveguide support structure 235 can support a portion of the waveguidespaced from the portion of the waveguide being acted upon by the sensorpad 232. In some implementations, the movement of the sensor pad 232 canresult in the flexing of the waveguide 212. FIG. 7B depicts animplementation where the sensing pad acts directly against the waveguideto result in a flexing of the optical waveguide 212. FIG. 7C depicts animplementation where a pressing portion 238 presses against a localizedportion of the waveguide. This can result in some compression combinedwith some flexing of the waveguide in an adjacent region. FIGS. 9A, and9B, discussed below, depict how the flexing of the waveguide 212 canresult in a reduction in the amount of light transmitted to the opticaldetector 240.

The optical sensing system 104 within the sensor frame 200 can act as amotion sensing system (e.g., a motion sensing system adapted to detectlocalized motion associated with an arterial pulse). The optical sensingsystem 104 within the sensor frame 200 can detect motion correspondingto an arterial pulse when the sensor fixation device is placed againstthe anatomical location of the subject, rather than merely a pressureapplied to the sensor pad 232. For example, a surface pressure sensor(e.g., a piezoresistive type pressure sensor) can detect changes inpressure due to an arterial pulse even when the pressure applied to theanatomical location by the occluding device 102 exceeds systolicpressure. At high cuff pressure (above systolic pressure) the arteryproximal to the occluding device 102 (e.g., an inflatable cuff) canimpart a pulsatile impact to the anatomical location delivered throughthe tissue, which causes a pulsatile pressure increase within theoccluding device 102. This effect causes a pulsatile tensioning of theoccluding device 102, which would be detected by a surface pressuresensor attached to the inside surface of the occluding device 102, eventhough there is no cuff contraction because the tissue is essentially“incompressible” and the artery is continuously occluded in the areaunderneath the pressure sensor. A signal of an amount of pressureapplied by the occluding device (i.e., a cuff bladder pressure sensor)and the surface pressure sensor will be similar above and below systolicpressure because the effect of the opening of the artery to allow bloodflow to occur is smaller than the effect of the pulsatile impact to thecuff described above. In contrast, an optical sensing system within asensor frame acting as a motion sensor can have little to no responsedue to the tensioning of the cuff at high cuff pressures and prevent thedetection of motion during arterial pulses at pressures above systolicpressure. Accordingly, the use of an optical sensing system within asensor frame as a motion sensor can more accurately indicate thesystolic blood pressure than a pressure sensor. Furthermore, no separateaccurate blood pressure measurement is needed for calibration orestablishment of a baseline.

Optical Sensing System using Optical Power Modulation

As shown in FIGS. 5C, 6, and 7A-7C, the optical sensing system 104 caninclude an optical source 202, an optical waveguide 212 and an opticaldetector 240. As discussed above, the optical sensing system 104 can beheld by a sensor frame 200 (e.g., a housing) held by the sensor fixationdevice 102. The optical source 202 can be optically coupled to theoptical waveguide 212, such that the optical energy (e.g., light waves218) travels from the optical source 202 into a first end of the opticalwaveguide 212. In some implementations, an LED can be used as theoptical source 202. An optical detector 240 receives the optical energyexiting an opposite, second end of the optical waveguide 212 and cangenerate a signal indicative of the amount of light received. In someimplementations, the optical detector 240 receives substantially all ofthe light exiting the second end of the optical waveguide 212. In someimplementations, the optical detector 240 can be a PIN diodephotodetector, a CCD (Charge-Coupled Device) detector, or a CMOS(Complementary Metal-Oxide-Semiconductor) detector.

Optical Waveguide

The optical waveguide 212 can be an optical fiber or any liquid, gel, orsolid that transmits light waves by internal reflection or refraction.An optical waveguide 212 can include a length of optically clearmaterial, commonly referred to as the “core” 215, which is surrounded bya material of lower refractive index, commonly referred to as the“cladding” 217. The core 215 can have a relatively high index ofrefraction (N₂), with respect to the lower index of refraction (N₁) ofthe cladding 217. The difference between the core and claddingrefractive indices defines the numerical aperture (NA) of the waveguide,according to the relationship:

NA=(N ₂ ²−N₁ ²)^(1/2)

It is the NA and the critical angle (θ_(c)) of a waveguide that governthe confinement of light within the core of the waveguide. If theincidence angle of a light ray at the core/cladding interface withrespect to a normal vector to the interface is less than the criticalangle (θ_(c)), then the ray will not be internally reflected but willescape the core and be lost. If N₂ is very close to N₁ (i.e., NA→0), thecritical angle will approach 90 degrees and nearly all the light willescape within a short length of waveguide. If N₂ and N₁ are sufficientlydifferent in value, a large portion of the light will remain confined.Optical energy (e.g., light) is lost from the optical waveguide when thelight wave reaches the interface between the two materials (the core 215and the cladding 217) at an angle less than the critical angle (θ_(c)).The critical angle (θ_(c)) can be calculated by the following equation:

θ_(c)=arcsin(N ₁ /N ₂)

Another characteristic of an optical fiber or optical waveguide is thenumber of modes that are excitable. In an optical waveguide, the term“mode” refers to a specific intensity pattern in a plane transverse tothe optical waveguide axis. A close relationship exists between theinternal mode pattern and the external speckle pattern of an opticalfiber. In a single mode fiber, only one intensity peak is allowed. Inmulti-mode fibers, a large number of intensity peaks may occur at anylocation along the waveguide. In any waveguide with circular crosssection, the “zero order” mode is formed by light propagating along thewaveguide axis (assuming a perfectly straight waveguide). So-called“higher order” modes are formed by light that is not launched in theaxial direction, but at some angle to the axis. These modes are guidedby the refractive index difference between the core and cladding andeach one will usually have lower intensity than the zero order mode.When a step index waveguide is flexed at some location, the lower orderand zero order modes become higher order modes because they no longerremain at or near the centerline. In order for light to occupy thehigher order modes in a waveguide, either the source of light must becomprised partly of light rays that are at a non-zero angle to the axis(but still within the numerical aperture of the waveguide), or else thewaveguide must be coiled or flexed. In general, few higher order modeswill exist in a waveguide that is illuminated by a collimated lightsource, and conversely a large number of higher order modes will existin a waveguide that is illuminated by a divergent light source.

As can be seen from FIGS. 8A, 8B, 9A, and 9B, the compression and/orflexing of a waveguide preferentially removes the higher order modes,and has relatively less effect on the lower order modes. The sensitivityof the optical system to small compressions and/or small amounts offlexing depend on the availability of a sufficient number of excitedwaveguide modes. For example, in a case of only five excited modes,theoretically only five different optical power transmission loss levelscould be detected, which would produce a rather coarse relationshipbetween deformation and the amount of optical detected by the opticaldetector of the optical sensing system. On the other hand, if there were10,000 excited modes, the relationship between deformation and detectedoptical energy could be much more finely determined and relatively smalldeformation changes could be detected. Accordingly, in someimplementations, the optical source can provide a diverging beam of anNA that is approximately equal to or greater than that of the waveguide.If the light source NA is greater than the waveguide NA, the result isthat the portion of the light emitted at the greatest angle of axisescapes into the cladding immediately. The optical waveguide can also beformed so that it is capable of guiding at least 10,000 modes (e.g.,greater than 50,000 modes). The number of possible modes in a step indexwaveguide is given by:

N=V ²/2

where V is the normalized frequency. The normalized frequency (V) iscalculated as follows:

V=2πa·NA/λ,

where a is the radius of the core of the optical waveguide, NA isnumerical aperture of the waveguide, as discussed above, and λ is thewavelength of light. The most practical light sources have a wavelength(λ) of between 0.7 to 0.85 micrometers. Consequently the product of aand NA must be on the order of 40 micrometers to satisfy the criteriafor 50,000 modes. The practical range of NA is 0.2 to 0.4 approximately.Accordingly, a waveguide having an NA of 0.4 would need to have aminimum of a core radius of 100 micrometers to allow for 50,000 modes,and a minimum radius of about 45 micrometers to allow 10,000 modes. Insome implementations, the waveguide core 215 has a radius of at least 45micrometers (e.g., between 150 and 200 micrometers). The optimum sizedepends in part also on the actual deformation encountered by thewaveguide (which is in turn dependent on the waveguide Durometer, themechanical pressure actually applied to the waveguide, and the amount offlexing of the waveguide). In some implementations, the waveguide canhave a soft elastomer core with Shore A Durometer between 45 and 55, anNA between 0.35 and 0.4 (corresponding to a core refractive index of1.46 and a cladding refractive index of 1.41), and core radius of150-200 micrometers. This design can produce a 50-70% transmission lossin a short length of waveguide (2-4 cm) when the flexing deformation isfrom 5-20 degrees over a length of 1-2 cm and/or where the core iscompressed by 5-50%.

An NA of 0.2-0.4 can be achieved by having a refractive index differencebetween core and cladding of 2-4% in common optical grade materials. Inlight transmission applications, light is introduced into one end of awaveguide. If the waveguide is straight, total internal reflection willcause confinement of all input light that is within the NA of thewaveguide, and the loss of light will be minimal. If a waveguide is notstraight but has some curvature, some of the light will undergo totalinternal reflection until it reaches a bend, where it arrives at thecore/cladding interface at less than the critical angle (θ_(c)) andescapes into the cladding. Similarly, if a waveguide is compressed, someof the light will undergo total internal reflection until it reaches acompressed area, where it arrives at the core/cladding interface at lessthan the critical angle (θ_(c)) and escapes into the cladding. Variabletransmission losses due to pulsatile bending or compression can bemeasured with an optical detector 240 (e.g., a photosensor) at theoptical waveguide exit and used to characterize the pulsatile forceacting on the waveguide.

As that shown in FIGS. 8A, 8B, 9A, and 9B, an optical waveguide 212causes the internal reflection of optical waves 218 within the core ofthe optical waveguide 212. However, the compression, as shown in FIG.8B, or the flexing, as shown in FIG. 9B, of the optical waveguide 212results in a loss of optical energy because the compression or flexingof the optical waveguide 212 results in additional light waves (such aslight wave 263) reaching the interface between the core 215 and thecladding 217 at angles less than the critical angle (θc). As shown inFIGS. 8A and 8B, the compression of the optical waveguide 212, resultsin a reduction in the transmitted optical energy 261, because of lostoptical energy 263. As shown in FIGS. 9A and 9B, the flexing of theoptical waveguide 212, results in a reduction in the transmitted opticalenergy 261, because of the lost optical energy 263.

The optical waveguide 212 can be flexible and/or compressible. In someimplementations, the optical waveguide 212 can include an elastomer. Forexample, the core 215, the cladding 217, or a combination thereof caninclude an elastomer. Conventional glass and plastic optical fibersexhibit bending losses, but are generally not deformable to asignificant extent by mechanical compression. Compliant waveguides,however, can be fabricated using softer materials. In contrast to glasswaveguides, such compliant waveguides may be easily deformed by smallcompression forces. Examples of suitable elastomers includepolysiloxane, polyurethane, and polybutadine rubber. In someimplementations, both the core 215 and the cladding 217 include asiloxane elastomer. For example, the optical waveguide can have acladding 217 composed of silicone elastomer and a core 215 composed of asecond silicone elastomer of different refractive index. In someimplementations, the cladding elastomer can be a material that does notinhibit the cure of the core material. For example, the claddingelastomer can have addition cure chemistry and the core elastomer canhave platinum cure chemistry.

The cladding 217 can be optically clear or can have a translucentappearance. The core 215 can be optically clear. In some embodiments,the cladding can have a refractive index between 1.39 and 1.48 (e.g.,between 1.39 and 1.41). In some embodiments, the core 215 can have arefractive index between 1.43 and 1.50 (e.g., between 1.45 and 1.47).The cladding can have a Shore A durometer of between 25 and 75 (e.g.,between 45 and 55). The core 215 can have a Shore A durometer of between25 and 75 (e.g., between 30 and 45).

The optical waveguide 212 can have a number of configurations. As shownin FIG. 10A, the cladding 217 can have a circular cross-sectional shape.In some implementations, the cladding can have a flat, widened bearingsurface along its length that can serve as an adhesive bonding surfacefor adhesion of the optical waveguide 212 to a flexible surface, forexample, a flexible circuit board used to support the optical waveguidewithin the optical sensing system. For example, the flat, widenedbearing surface can be bonded to a waveguide support surface by aflexible elastomer adhesive. FIGS. 10B-10D show cross-sections ofexamples of optical waveguides 212 having a flat, widened bearingsurface 271.

The cladding 217 of the optical waveguide 212 can be formed by anextrusion process. In some implementations, the core 215 and thecladding 217 can be formed in a co-extrusion process. In someimplementations, the cladding 217 can be extruded in a first process toproduce a constant cross-sectional shape defining a hollow lumen. Thecore 215 can then be made by filling the lumen of the cladding 217 witha core material. For example, an extrusion process can be used to makeany of the cladding cross-sectional shapes shown in FIGS. 10A-10D. Insome implementations, the location of the core centerline may be set tomatch the location of the exit beam of the optical source 202, after theoptical source 202 and optical waveguide 212 are mounted on the flexiblewaveguide support 235, thereby facilitating ease of optical alignment ofthe optical waveguide 212 to the optical source 202.

Analytical Methods

The optical detector 240 of an optical sensing system 104 can generatean electrical signal 420 indicating the amount of light received. Theelectrical signal 420 can be a function of time. The electrical opticaldetector signal 420 is analyzed to determine a number of vital signs.The output unit 106 can determine the amplitude and/or magnitude of eacharterial pulse to determine one or more vital signs. In someimplementations, the amplitudes and/or magnitudes for a series ofarterial pulses can be determined to determine one or more vital signs.In some implementations, the time interval between pulses can bemeasured during a series of detected arterial pulses and used todetermine heart rate. For example, FIG. 11 demonstrates the pulsatilelight transmission in a waveguide subjected to an oscillatingdeformation due to an arterial pulse. Some vital sign measurements, suchas a heart rate, do not require input regarding the pressure applied tothe anatomical location by, for example, a pneumatic cuff.

Blood pressure, for example, can be measured by placing the cuff (e.g.,as shown in FIG. 4) on a patient's arm; inflating the cuff to a pressureat least 10 mmHg higher than the patient's systolic pressure; graduallydeflating the cuff pressure to a pressure at least 10 mmHg belowdiastolic pressure; recording the arterial pulse waveforms produced bythe optical sensing system 104; analyzing the waveforms to determine oneor more features that correspond to systolic pressure; further analyzingthe waveforms to determine one or more features that correspond todiastolic pressure; fully deflating the cuff; and displaying thesystolic and diastolic pressure. In some implementations, the waveformscan be recorded both during inflation and deflation of the cuff and bothwaveforms be used to determine systolic and/or diastolic pressure.

By observing the arterial waveform formed through this process, variousvital signs can be determined and/or estimated, such as systolicpressure, diastolic pressure, and mean arterial pressure. In someimplementations, the method of measuring blood pressure can includeanalyzing the arterial pulse waveforms by measuring the amplitudes ofthe sequence of waveforms recorded during the cuff deflation;determining the cuff pressure at which the pulse waveform amplitude issignificantly higher than the waveform amplitude of the preceding pulseoccurring at higher cuff pressure during deflation of the cuff; anddisplaying that pressure as the systolic pressure.

Systolic pressure can be determined in a number of ways based on thedata received from the optical sensing system 104 and from data from thesensor fixation device 102. In some implementations, the systolicpressure can be determined at the cuff pressure at which the pulsewaveform amplitude is significantly lower than the waveform amplitude ofthe preceding pulse occurring at lower cuff pressure during inflation ofthe cuff. In some implementations, the diastolic pressure can bedetermined during deflation of the cuff at the cuff pressure where thepulse waveform is indicative of the pulsatile action of the arterialsegment under the sensor. More specifically, the diastolic pressure canbe determined where the pulse waveform first indicates that the arterydoes not fully close at any time during the cardiac cycle. Differentmethods of waveform analysis are also possible. A patient's systolicblood pressure can also be continuously monitored by measuring thebaseline systolic pressure by one of the methods described above andthen pressurizing the cuff to a constant pressure and then continuouslymonitoring the waveform. The constant pressure can be determined by thepreviously measured blood pressure reading (e.g., peak arterialpressure). A first measured arterial pulse amplitude can then be used asa reference pulse amplitude and subsequent pulse amplitudes can becompared to that reference pulse amplitude to estimate changes in bloodpressure. In some implementations, the pulse waveform morphology can bedetermined for pulses while the cuff is held at the constant pressure.The pulse waveform morphology can be measured continuously and used tomonitor blood pressure changes relative to a baseline value.

In some implementations, such as shown in FIG. 12 the output unit 106can determine a vital sign by one or more of the above describedtechniques. For example, the output unit 106 can determine an amplitude,a magnitude and/or a waveform of one or more arterial pulses in awaveform generator 436. In some implementations, the output unit 106 caninclude a systolic pressure calculator 442 to determine a systolicpressure for a subject based upon a determined amplitude, magnitudeand/or waveform and a pressure applied to the subject, which can bedetected (e.g., a pressure detected in an inflatable cuff by a pressuresensor). In some implementations, the output unit 106 can include adiastolic pressure calculator 444 to determine a diastolic pressure fora subject based upon a determined amplitude, magnitude and/or waveformand a pressure applied to the subject, which can be detected (e.g., apressure detected in an inflatable cuff by a pressure sensor 128). Insome implementations, a heart rate calculator 446 can determine a heartrate from either a determined arterial pulse waveform from the opticalsignal or from pressures detected in an inflatable cuff by a pressuresensor 128.

The output unit 106 shown in FIG. 12, also includes a pressure sensor128 pneumatically connected to a bladder in the cuff, which transmitsdata regarding the pressure in the cuff as a function of time to theanalog-to-digital converter 435. In some implementations, the outputunit 106 can generate a pulse waveform as a function of cuff pressure.The output unit 106 shown in FIG. 12 also includes an inflationcontroller 452, which can control the inflation and deflation means ofthe cuff to control the operation of the device. In someimplementations, the output unit 106 can dynamically adjust theinflation and deflation of the cuff based on detect arterial pulsecharacteristics.

A number of implementations have been described. Nevertheless, it willbe understood that various modifications can be made without departingfrom the spirit and scope of the invention. Accordingly, otherimplementations are within the scope of the following claims.

1. A vital sign measurement device comprising: a sensor fixation deviceadapted to be placed against an anatomical location of a subject, withinwhich is an artery; a sensor frame held by the sensor fixation device,an optical sensing system held by the sensor frame and comprising anoptical waveguide, an optical source device to supply optical energy toa first end of the optical waveguide, and an optical detector to detectan amount of optical energy exiting the second end of optical waveguide,the optical sensing system adapted to sense an arterial pulse from thecompression or flexing of at least a portion of the optical waveguideresulting in reduction of the amount of optical energy exiting thesecond end of the optical waveguide; and an output unit configured toreceive a signal indicative of the amount of light exiting the secondend of the optical waveguide and to generate a measure of the vital signbased at least in part on the received signal.
 2. The vital signmeasurement device of claim 1, wherein the sensor fixation device is acuff comprising an inflatable bladder adapted to apply pressure to thelimb when inflated and thereby compress the artery within the limb. 3.The vital sign measurement device of claim 1, further comprising apressure sensor to detect a pressure applied to the anatomical location,wherein the output unit receives a pressure input indicative of thepressure applied to the anatomical location from the pressure sensor,and wherein the output unit generates the vital sign using the signalindicative of the optical signal received and the pressure input.
 4. Thevital sign measurement device of claim 1, wherein the anatomicallocation of the subject is an upper arm, and the sensor frame isconfigured on the sensor fixation device so that the optical sensingsystem is positioned to sense movement due to a pulse of a brachialartery resulting in the compression or flexing of at least a portion ofthe compressible optical waveguide.
 5. The vital sign measurement deviceof claim 1, wherein the optical waveguide comprises an elastomer.
 6. Thevital sign measurement device of claim 5, wherein the elastomer isselected from the group consisting of polysiloxane, polyurethane,polybutadine rubber, and combinations thereof.
 7. The vital signmeasurement device of claim 1, further comprising a waveguide supportstructure comprising a non-compliant surface, the waveguide supportstructure supporting at least a portion of the optical waveguide.
 8. Thevital sign measurement device of claim 1, further comprising a flexibleand incompressible support surface that supports the optical waveguideover substantially all of its length.
 9. The vital sign measurementdevice of claim 8, wherein the optical source device and the opticaldetector are mounted on the surface of the waveguide support surface.10. The vital sign measurement device of claim 1, wherein the opticalsensing system is configured to detect optical signals representative ofa series of arterial pulses and the output unit is adapted to determinea pulse waveform for each of the series of arterial pulses.
 11. Thevital sign measurement device of claim 1, wherein the optical detectoris optically coupled to optical waveguide such that the optical detectorreceives substantially of the optical energy from the optical sourcethat does not escape from the sides of the optical waveguide.
 12. Thevital sign measurement device of claim 1, wherein the vital sign is atleast one of a heart rate, an arterial pulse waveform, a systolic bloodpressure, a diastolic blood pressure, a mean arterial blood pressure, apulse pressure, and an arterial compliance.
 13. A method of measuring avital sign in a subject, the method comprising: transmitting opticalenergy into a first end of an optical waveguide, the optical waveguidepositioned with a sensor frame, the sensor frame positioned against ananatomical location of a subject, within which is an artery, the opticalwaveguide positioned to compress or flex in response to an arterialpulse; detecting, using an optical detector held by the sensor frame, anamount of optical energy exiting a second end of the optical waveguideand generating therefrom a signal indicative of optical energy received,the amount of optical energy exiting the second end of the opticalwaveguide changing in response to an arterial pulse; and generating ameasure of the vital sign using the generated signal indicative of theoptical energy exiting the second end of the optical waveguide.
 14. Themethod of claim 13, wherein the vital sign is at least one of a heartrate, an arterial pulse waveform, a systolic blood pressure, a diastolicblood pressure, a mean arterial blood pressure, a pulse pressure, and anarterial compliance.
 15. The method of claim 13, wherein the sensorframe is held by a sensor fixation device, the method furthercomprising: applying a pressure to the anatomical location of thesubject with the sensor fixation device.
 16. The method of claim 15, themethod further comprising: varying the pressure applied to theanatomical location with the sensor fixation device over a period oftime; and determining a series of pulse characteristics for arterialpulses during the period of time from changes in the amount of opticalenergy exiting the second end of the optical waveguide over the periodof time, wherein the generated measure of the vital sign is based on theseries of pulse characteristics during the period of time.
 17. Themethod of claim 15, further comprising obtaining a measured bloodpressure measurement; obtaining an initial pulse characteristic, at aninitial time, and a subsequent pulse characteristic, at a subsequenttime, using an input indicative of the amount of optical energy exitingthe second end of the optical waveguide, wherein the measured bloodpressure measurement was obtained at a measurement time closer to theinitial time than to the subsequent time, wherein the generatedmeasurement of the vital sign is based on the measured blood pressuremeasurement, the initial pulse characteristic, and the subsequent pulsecharacteristic.
 18. The method of claim 17, wherein the initial pulsecharacteristic and the subsequent pulse characteristics comprise pulseamplitudes.
 19. A method of measuring a subject's blood pressure, themethod comprising: applying a varying pressure to an anatomical locationof a subject, within which is an artery; detecting an arterial pulsewaveform with an optical power modulation sensor as a function of theapplied and varied pressure, the optical power modulation sensorincluding an optical waveguide adapted to be compressed or flexed inresponse to an arterial pulse, the compression or flexing of the opticalwaveguide resulting in a reduction in the amount of light transmitted toan end of the optical waveguide, the arterial pulse waveform beingdetected from the amount of light exiting the end of the opticalwaveguide; and determining a systolic blood pressure and a diastolicblood pressure based on the detected arterial pulse waveform as afunction of the applied and varied pressure.